Manufacturing operations often involve a variety of resources, processes, and buffers. The main resources in the manufacturing environment are operators and machines. The processes transform items, such as intermediate products, into final products or other intermediate products and the buffers hold the items. Each process has an associated cycle time, or processing time, indicating how long it takes to convert input items to the produced, or output, items. The buffers are characterized, for example, by a maximum capacity and an inventory level.
Some processes operate continuously, whereas other processes operate as needed and/or as scheduled. Each process may be performed by one or more machines; each machine may be dedicated to performing one type of process or may be capable of performing a number of different processes. In addition, a number of machine types may be available to perform a particular process with different throughputs, processing times, and the like.
Each machine may require one or more human operators during at least some part of the process. For example, a human operator may be needed to load the machine, operate the machine, monitor the machine, unload the machine, service the machine, and the like. Each human operator may be capable of operating all of the machines in the manufacturing environment, or only a subset of the machines. Thus, the scheduling of human operators and machines has an important effect on the overall performance of the manufacturing environment, including parameters such as total throughput and manufacturing time.